Current impulse transformer



April 15, 1941. v. T. FARE 2,238,185

CURRENT IMPULSE TRANSFORMER Original Filed March 31, 1937 Patented Apr.15, 1941 UNITED STATES PATENT OFFICE CURRENT IMPULSE TRANSFORMER VictorT. Par, Collingswood, N. 1., assignor to Radio Corporation of America, acorporation of Delaware 5 Claims.

This application is a division of application Serial No. 133,965, filedMarch 31, 1937.

This invention relates to transformers, particularly to so-calledcurrent impulse transformers and to circuits and apparatus forenergizing and controlling the same.

Current impulse transformers capable of generating relatively highmomentary values of direct current find useful application, for example,in the art of magnetizing permanent magnets.

A current impulse transformer may comprise a primary winding of manyturns, a secondary of few turns (usually one), and an intermediate ironcore. Direct current is fed to the primary winding in an amountsufficient substantially to saturate the iron core. If the circuit tothe primary winding now be opened, the energy stored in the core will besuddenly released. A portion of this energy will appear in the secondarycircuit (if it is closed) as a direct current impulse, and the balancewill appear in the form of an are between the opened terminals of theprimary circuit. Since only the direct current impulse in the secondarycircuit is usefully employed, it follows that the efficiency of thedevice is proportional to the quantity of energy dissipated in the formof an arc between the open terminals of the primary circuit, that is tosay, the less energy dissipated in the primary circuit, the more is theuseful energy appearing in the secondary circuit. It is apparent fromthe foregoing that the more rapidly the primary circuit is opened, andthe more rapidly and completely the resulting arc is quenched, thegreater is the energy available in the form of a direct current impulseon the secondary side of the transformer.

In order to ensure a rapid break and adequate quenching of the developedarc, resort has heretofore been had to circuit breakers of the typecomprising a fast acting switch having contacts immersed in anarc-quenching magnetic field. The usual practice has been to provide amultiple contact switch and to so arrange the connections thereto thatupon opening of the primary circuit the current from the line isswitched to the coils which then, and not until then, generate thearc-quenching magnetic field. Regardless of the advantages claimed forthe described conventional type of circuit breaker,

before the flux of the magnetic field has been built up to the densityrequired to ensure proper quenching.

Accordingly, an object of the present invention is to provide a circuitfor use in connection with iron core transformers and including meansfor preventing the actuation of said device until the energy in saidcore is built up to the value required to accomplish a given task,whereby wasteful dissipation of energy is obviated.

Another object of the invention is to provide a circuit for a currentimpulse transformer system of the type wherein direct current flowing inthe primary circuit gives rise to energy in the core of saidtransformer, said system including means adapted to open the primarycircuit quickly and cleanly, whereby the energy released upon thecollapse of the magnetic forces stored in the core may be efficientlytransformed into current of optimum value in the secondary of saidtransformer.

Other objects and advantages, together with certain details ofconstruction, will be apparent and the invention itself will be bestunderstood by reference to the following specification and to theaccompanying partly diagrammatic, partly elevational View of a currentimpulse transformer system embodying the invention.

In this drawing, l designates generally a current impulse transformercomprising a primary winding 3, an iron core 5 and a secondary winding'1. Winding 1 terminates in a pair of bus bars 9. By way of example, theprimary winding 3 may comprise twenty-five hundred turns and thesecondary l but one turn. The energy applied to the primary 3 oftransformer I may be obtained from a 220-volt 24-ampere source of directcurrent. Such source is indicated in the drawing by the conventionalplus and minus symbols.

The application of direct current to the primary 3 stores up magneticenergy in the iron core 5. When this core becomes saturated, orsubstantially so, and the circuit supplying current to the primary isthen broken, a momentary direct current surge or impulse will appear inthe secondary I, provided its terminals 9 are closed. This impulse mayreach a value of, say, fifty-five thousand (55,000) amperes providedonly that too much of the magnetic energy stored in core 5 is notdissipated in the form of an are between the points at which the primarycircuit is broken. Current of the order or value mentioned may beutilized, for example, to permanently magnetize metal objects, in whichcase magnetic field generated about core 5.

the object to be magnetized (not shown) may be removably clamped to busbars 9.

A switch, indicated gene-rally at l I, is provided for opening thecircuit carrying current to the primary winding 3 of transformer l.Switch II comprises a frame l3 which supports a fixed switch arm i5 anda movable switch arm l'l. Arm I! is biased to open as by means of aspring l9 and may be held in the closed position as by means of a pawl 2I, which is urged into engagement with arm I! by means of a. spring 23.

Switch arms l5 and I! are provided with contacts and 21, respectively.In order to quench or "blow-out the arc incident to the opening of theswitch, contacts 25 and 21 are immersed in a magnetic field whichbridges the pole pieces 29 and 3| of an electro-magnet M. Thearrangement of these pole pieces may, if desired, be similar in allrespects to that described in connection with the modified form ofswitch shown in Fig. 2 of the previously-identified par ent applicationSerial No. 133,965.

In order to prevent the opening of contacts 25 and 21 until the fluxdensity of the magnetic field reaches 'a value sufficient to insureprompt and adequate quenching of the arc between these contacts, amagnetically actuated mechanism is provided for releasing the pawl 2!which holds the movable switch arm in its illustrated closed position.Such mechanism may be constituted essentially of an armature 33 composedof a magnetically permeable material secured to a plunger 35 which isslidable in an extension 31 in frame i3 and connected to pawl 2| by anadjusting screw 39. As illustrated, the armature 33 and plunger '35 arein that position whereat pawl 2| holds switch arm I! closed against thetension of spring 18. It will be understood that spring 23 of therelease mechanism is so adjusted that when the fiux density of themagnetic field in which contacts 25 and 21 are immersed reaches a valuesufficient to adequately quench the arc developed upon opening of thesecontacts then armature 33 will be pulled down against the tension ofspring 23 causing pawl 2| to pivot out of engagement with the end ofswitch arm I? and permitting it to be instantly and forcibly pulledoutwardly by spring l9. A switch handle 4! is provided for returningswitch arm I! to its illustrated closed position with respect to arm I5.

As previously set forth, the surge of current across terminals 9 of thesecondary 1 of transformer I when the magnetic energy stored in core 5is released must be of a certain high value to perform its task. If thecircuit to primary 3 were to be opened before core 5 stored up enoughene'rgyto provide secondary 7 with current of a value less than thatrequired, much energy, as well as the 'operators time, would be wasted.To obviate such waste, an auxiliary control is provided in conjunctionwith the release mechanism of switch ll whereby premature opening of thecircuit to the primary winding 3 of the transformer l is prevented.

The illustrated auxiliary control comprises a pair of switches 43 and 59connected in series in the circuit which provide energy for generatingthe arc-quenching magnetic field. Switch 13 may comprise a stationaryarm 45 and a pivoted arm 47 shown biased to the open position by aspring 49. A separate pivoted arm 5| supports an armature 53 ofmagnetically permeable material adjacent and within the influence of theArm 5| is provided with a snubber 55 and is normally held by a spring 51in a position such that its armature 53 is out of the region of maximumintensity of the field adjacent core 5.

As the energy transferred to core 5 from primary I is built up, armature53 is gradually attracted thereto and pushes arm 41 over (to the left asviewed in Fig. 1) against the tension of spring 43. This brings arm 41in contact with arm 45 and thereby completes the circuit to switch 59.Switch 53 may be of conventional design and comprises a solenoid [itwhich when energized attracts an armature 53 closing contacts and 61.

In operating the device of Fig. 1, the switch arms I5 and ill of switchII are first closed by means of the switch handle 4|. Arm I! carryingcontact 21 is thus locked in its closed position by pawl 2i, andarmature 33, which controls the release of pawl 2i, and hence of arm i1,is in its idle or raised position. The circuit to this switch H may nowbe traced from the positive side of the 220-volt line through lead a,primary winding 3, arm 55, contacts 25 and 21 to movable switch arm I!and through lead 2) to the negative side of the current source.

Current flowing through the primary winding 3 stores magnetic energy incore 5. When core 5 is saturated, or substantially so, it attracts thearmature 53 of switch 43, and moves pivoted arm 5! which in turn movescontact 41 against the tension of spring 49 into contact with arm :35.Contacts 45, 47 being thus closed, the solenoid SI of switch 59 isenergized and its contacts 55 and 67 are closed. Current now flowsthrough branch line 0 through contact 61 to the electromagnet M, andthrough lead e to contacts 55 from whence it flows through wire back tothe return lead I) to the negative side of the di rect current source.

Contacts 25 and 21 are maintained closed by pawl 2| until armature 33,on plunger 35, is pulled down. Armature 33 can be pulled down to releasethe pawl 2i and the spring biased switch arm I! only when the fluxdensity of the magnetic field in which contacts 25 and 21 are immersedreaches a value sufiicient to quench the arc incident to the opening ofthese contacts. As previously set forth, prompt and adequate quenchingof the are between contact 25 and 21, such as is provided by theimproved mechanism of the present invention, ensures that energyreleased upon the collapse of the magnetic forces stored in the ironcore 5 will be converted into current of optimum value in the secondaryor output 3 of the current impulse transformer I.

Various modifications of the invention will suggest themselves to thoseskilled in the art. It is to be understood therefore that-the scope ofthe invention is not to be limited except as required by the prior artand by the spirit of the appended claims.

What is claimed is:

1. In a device of the character described, a source of current, atransformer connected to said source, a switch connected between saidsource and said transformer, means for generating a magnetic fieldwithin which the contacts of said switch are immersed, means foractuating said switch, and means for delaying the operation of saidswitch actuating means until the electrical energy in said transformerand the flux density of said magnetic field reach predetermined values.

2. In apparatus of the character described, a source of direct current,a current impulse trans former connected to said source, a switchconnected between said source and said transformer, means responsive toan electrical condition of said transformer for generating an arcquenching magnetic field adjacent the contacts of said switch, and meansresponsive to the intensity of said magnetic field for controlling theactuation of said switch.

3. In apparatus of the character described, an iron core transformer, asource of direct current connected to the primary winding of saidtransformer, a switch between said source and said winding, meansresponsive to an electrical condition of said iron core for generatingan arc quenching magnetic field adjacent the contacts of said switch,and means for opening said switch when said are quenching magnetic fieldreaches a predetermined intensity.

4. In apparatus of the character described, a controlling and acontrolled circuit, a switch arm in said controlling circuit, meansbiasing said switch arm to its open position, means for holding said armclosed against the force of its bias, means connected to saidcontrolling circuit for deriving current from said controlled circuitand for producing an arc quenching magnetic field adjacent said switcharm, and means responsive to a predetermined flux density of saidmagnetic field for releasing said holding means.

5. In apparatus for magnetizing objects, a source of direct current, aniron core transformer having a primary terminal connected to said sourceand a secondary terminal to which a magnetizable object may be attached,a switch connected between said source and the primary of saidtransformer, a pair of pole pieces adjacent the contacts of said switch,a second switch having an actuating member mounted adjacent saidtransformer and adapted to close when the electrical energy in the saidcore of said transformer reaches a value calculated to be sufiicient tomagnetize said object, means responsive to the closing of said secondswitch for producing an arc quenching magnetic field between said polepieces, and means for delaying the opening of said firstrnenticnedswitch until said magnetic field reaches a value sufficient toextinguish the are developed between its contacts incident to theopening of the circuit between said source and the primary of saidtransformer.

VICTOR T. FARE.

